code: def test_no_classes_raises(self):
      X, y = dask_ml.datasets.make_classification(chunks=25)
      clf = dask_ml.ensemble.BlockwiseVotingClassifier(
          sklearn.linear_model.LogisticRegression(solver="lbfgs"),
      )
      with pytest.raises(ValueError, match="classes"):
          clf.fit(X, y)
  
file_path: dask-ml/tests/ensemble/test_blockwise.py
imports: import dask
  import dask.array
  import dask.dataframe
  import numpy
  import pytest
  import sklearn.linear_model
  import dask_ml.datasets
  import dask_ml.ensemble
label_desc: Use image node_id 6 for calling the TestBlockwiseVotingClassifier obj's underlying member method code with example usage: obj.test_no_classes_raises() without return types